A Scientist’s Best Friend: The Biology Behind The Human-Dog Relationship

Kristen Blanchard

Originally published April 7, 2015

photo by: kristen thomas

photo by: kristen thomas

If you had visited Tokyo’s Shibuya Station in the 1920s, chances are, you would have met Hachikō. At the end of every day, this purebred Akita Inu faithfully waited for the train to deliver his master, Hidesaburō Ueno. Yet, when Ueno died in May 1925, Hachikō continued to wait. For the rest of Hachikō’s life (nine years, nine months, and fifteen days to be exact), Hachikō continued to arrive at the station and wait for his owner’s train. Hachikō may be the most famous symbol of canine loyalty, but he is by no means alone. Capitán, a German Shepherd in Argentina, stayed with his owner’s grave for 6 years after he passed. Orlando, a black lab guide dog in New York City, helped save his owner from an oncoming subway train after the man fell onto the tracks. In addition to these “celebrity” dogs, we rely on countless others to help us track missing persons, locate explosives, and help those with disabilities. In return for their services, we love these creatures like no other on the planet. More than one third of American households own a dog, and we spend more than $50 billion annually on our pets. It seems obvious that dogs are man’s best friend, but why does the bond between man and dog seem so different than any other animal?

The answer to this question likely lies in dogs’ unique history. Domesticated dogs, as we know and love them today, evolved from ancient wolves. Unlike the evolution of virtually every other animal species throughout history, the evolution of dogs was artificial. Humans essentially “created” this species by domesticating wolves. Through lucky accidents in different regions throughout the planet, ancient humans noticed that some wolves were more cooperative than their peers. They took in these unusually helpful wolves, cooperating to hunt prey and avoid predators. Biologists believe that by continually selecting for better companions, wolves and humans evolved side-by-side, eventually creating the unique bond between modern humans and dogs.

This strong evolutionary pressure has had significant consequences for the way humans and dogs interact. In the past few decades, scientists have been able to quantify what dog lovers have long understood on an intuitive level; the bond between canines and humans is unique among the animal kingdom. Scientists have demonstrated that dogs are adept at communicating with humans. They can pick up on auditory cues and even physical signals. Dogs understand the meaning behind human pointing, while even our closest relatives, great apes, cannot interpret this gesture. Despite the fact that great apes are more intelligent than dogs, and more closely related to humans, dogs are better at communicating with us. This communication skill goes beyond merely communicating basic information. Some evidence shows that dogs can understand human emotion. Scientists at the University of Veterinary Medicine in Vienna, Austria tested dogs for their ability to recognize human facial expressions. The study found that dogs could distinguish between “happy” human faces and “angry” human faces, even while only seeing part of the face in a photograph.

photo by: kristen thomas

photo by: kristen thomas

What do dogs do with this information about human emotion? Do they “care” if a human is happy or angry? Do dogs have some sort of empathy with their human companions? Scientists have recently tried to answer these questions as well. Contagious yawning (i.e., the tendency to yawn when witnessing someone else yawn) is thought to be a sign of empathy. Contagious yawning is usually more common between people who are emotionally close, than between strangers. Scientists at The University of Tokyo recently investigated whether dogs were also affected by the contagious yawning phenomenon. They found that not only did dogs exhibit contagious yawning when seeing humans yawn; this effect was also more common between the dog and its owner than the dog and a stranger. These results suggest that dogs do display this measure of empathy.

The idea that dogs possess empathy for their human companions is further supported by an interesting study by researchers at the University of Otago in New Zealand. These scientists measured the human physiological response to a baby crying. Humans respond to this trigger with an increase in cortisol and heightened alertness. Fascinatingly, they discovered that a human baby crying affected dogs in the same way. In addition to the increase in cortisol and heightened alertness, dogs also became more submissive. While it is difficult to quantify whether or not dogs “love” their human companions, there is certainly some evidence that dogs have empathy for humans and an understanding of human emotion.

But what about the other side of this relationship? It certainly seems as though humans’ artificial selection of ancient wolves contributed to the way dogs relate to humans today. Were humans also affected by this parallel evolution? Is the bond between humans and dogs hard-wired into us the way it seems to be in dogs? Some recent studies suggest that this evolution was a two-way street; just as dogs evolved to cooperate better with us, we evolved to cooperate better with them. While dogs are adept at recognizing human facial expressions, we are adept at recognizing theirs as well.  A recent study found that even people without any experience with dogs were able to infer a dog’s emotion from a photograph. The fact that even those without dog experience were able to complete this task suggests that this recognition may be innate – an artifact from our co-evolution with domesticated dogs.

Fortunately for us, while dogs may have influenced our evolution, it seems to be worth the tradeoff. Our relationship with dogs provides us numerous benefits as a species. Dogs have a well-documented effect of reducing stress. The American Heart Association has even reviewed the scientific literature and agreed that dog ownership may slightly reduce the risk of heart disease. These health benefits explain why dogs are frequently used as therapeutic aids – they can help soldiers recover from trauma and help children with autism improve in socialization. Thanks to our truly unique interspecies bond, these creatures really are man’s best friend.

Edited by: Bethany Wilson